Canister for cast primer



G. L- GRIFFITH CANISTER FOR CAST PRIMER May 18, 1965 2 Sheets-Sheet 1 Filed Aug. 21, 1965 FIG. 4

FIG. 1

FIG. 5

I n ve n t o r George L. Griffith his A orney May 18, 1965 GRIFFITH CANISTER FOR CAST PRIMER Filed Aug. 21, 1963 2 Sheets-Sheet 2 FIG. 6

FIG. 10

In v e n to r George I... Griffith United States Patent 3,183,836 CANISTER FOR CAST PRIMER George L. Griffith, Coopershurg, Pa., assignor to Trojan Powder (Zompany, Allentown, Pa.., a corporation Filed Aug. 21, 1963, Ser. No. 303,533 7 Claims. (Cl. 102-24) This invention relates to blasting, particularly to means for priming or 'boostering the charge in a borehole. Its principal object is to provide a primer canister that lends itself readily to automation in both its formation and in the filling of the canister.

Another object of the invention is to provide a canister that consists of only two parts, each of which is a single piece of suitable conductive or semi-conductive and nonstatic producing material preferably polypropylene, but including polyethylene, polyolefins, and Where heat resistance or impact strength at low temperatures is required, copolymers such as .those of polyethylene-polypropylene are found suitable. One of the two pieces includes a tube or well passing through the canister so as to accommodate a continuous length of Primacord and a second well having a closed end within the canister and an end open at the canister surface so that a blasting cap may be inserted in the canister after it has been filled and the two parts are locked together.

A further object of the invention is to provide a canister having Walls so thin as to insure initiation of the primer charge While avoiding the danger of having the wall of either well leaking molten primer material into the well and consequently interfering with, if not absolutely blocking, passage of the Primacord or the blasting cap into its proper place in the container.

Still further objects of the invention relate to details such as locking the cover to the container and flaring the entrance ends of the wells to avoid sharp corners in the cast primer material, preferably pentolite. This flaring to an acceptable radius of curvature at the entrance ends is important from a practical point of view as it avoids sharp corners on the outside of the canister and clearly reduces the possibility of severing the Primacord downline and/or electrical cap leg wires during the loading operation. While a solid priming material is preferred, a liquid or semi-liquid, or a gel may be used; for example, slurries, TMETN compositions, Nitrostarch/DNT mixtures, etc.

In the drawings:

FIGURE 1 is a central section through a canister;

FIGURE 2 is a bottom plan view;

FIGURE 3 is a horizontal section taken near the bottom of the canister;

FIGURE 4 is a vertical section through the top of the Primacord well after it has been swaged over the cover in order to lock the latter to the container;

FIGURE 5 is a radial section through an upper corner of the canister showing additional means for locking the cover to the container;

FIGURE 6 is a central section; FIGURE 7 is a top plan; and FIGURE 8 is a bottom plan of a modification;

FIGURE 9 is a top plan; and FIGURE 10 is a bottom plan of a further modification;

FIGURE 11 is a section on line 1 1-11 of FIGURE 9; and

FIGURE 12 is a section on line 12-12of FIGURE 9.

In the experimental stage of this invention, dificulty was met because in forming the wells, the liquid polypropylene tended to flow less freely as it rose to the top of the well. This sometimes restricted the amount of plastic flowing and hence holes were formed in the side of the wall as the latter became thinner. These holes are highly objectionable because during the filling of the container, the hot pentolite primer material would flow ice through such imperfect walls of the wells and would create an obstruction inside of the Wells sometimes making it impossible to feed the Primacord through the longer well or tube or to place the blasting cap in the shorter we 1.

This difliculty has been avoided by adding from three to seven fins spaced equally about the outside of the two wells. As these fins, preferably four in number, are formed by grooves in the die, ample plastic flows up into the tops of the tubes and insures that the walls at the top of the wells shall be ample in thickness, at least .005" with a preferred wall thickness between fins being .020". A materially thicker wall than the latter figure would require use of a more sensitive explosive in the canister and this obviously is objectionable because of the added hazards. Where a suitable higher melting point material is available the wall may be thinner than the preferred figure stated, thus increasing the sensitivity of the primer unit consequently increasing the dependability of the unit when used with standard or conventional initiators.

The canister 10 consists of but two parts, a container 11 and a cover 12, the latter having a flat top 14 (FIG. 5) with a thickened rim 15 engaging the outwardly flared top 16 of the container. A groove 17 is located near the top of the container to receive an annular rib 18 on the outside of the downturned flange 19 of the cover to aid in locking the cover to the container as later explained.

The container is in the general form of a water tumbler or drinking glass but has two integral wells 20 and 21 which rise from its fiat bottom. The bottom 22 is rounded as at 23 to correspond with the important rounded junctions 24 and 25 of the wells, and for the same purpose, that is, to avoid a sharp edge on the solid mass of pentolite which edge might tend to cut the polypropylene of the container should there be any looseness. The radius of curvature is preferably about one-third of the diameter of the wells. Each of the two wells is slightly tapered, the wells being larger at their bottoms than at their tops, this to facilitate formation of the container and its removal from the die.

The longer Well 26 extends a sufficient distance above the level of the top 14 of the cover, as shown slightly exaggerated at 26, in order to allow for spinning or swaging this extended portion over the top of the cover as illustrated at 27 in FIGURE 4. This arrangement with the rib and groove connection shown in FIGURE 5 securely locks the cover to the container after latter is filled. The inwardly projecting flange 33 of the cover preferably has an inside conical surface 34, the better to receive and guide the top 26 of the tube 20 in mass production assembly. The shorter Well 21 preferably extends upward from the bottom of the container rather than downward from the cover 12 and in either event its end inside of the canister is closed as at 29.

Referring now to FIGURE 3 the walls of both Wells are provided with integral splines or fins such as 30 extending the entire length of the tube. The number of fins may vary from three to seven but four as illustrated seem preferable and this number has been found ample. For clarity of illustration the size of these fins is exaggerated as is also the radial dimension of the wall between fins, the wall thickness 31 between fins being as previously stated in the neighborhood of a fiftieth of an inch which provides the thinness required to insure proper detonation of a primer material of suitable sensitivity by either the blasting cap or the Primacord, neither being shown.

The canister as shown is used at a rate of about one to each ten feet of the charge and can readily detonate relatively insensitive explosive material. While pentolite is the preferred priming material, the invention is not limited to solid priming charges as liquids, semi-solids, and gels 3 such asTMETN compositions, slurries, Nitrostarch/DNT mixtures, etc., may be used.

The modification shown in FIGURES 6 to 8 differs only in that annular V-shaped troughs 35 and 36 are provided in the cover and in the container to give a shaped charge effect. The troughs are located adjacent the cylindrical side 33 of the canister, and are parallel thereto. The apex angle is between 40 and 70.

The same effect is produced by the canistor of FIG- URES 9 to 12 in which the troughs are replaced by conical depressions 38 between four and ten in number and having an apex angle between 40 and 70".

What I claim is:

l. A canister for cast primers suitable for mass production and automatic filling, comprising a container and a cover for the container; said container being a one-piece body with an open end for receiving the primer material and a closed end, there being two walled wells in the container, one to receive a Primacord passing longitudinally through the canister and the other a parallel well to house a blasting cap, the Primacord well extending from the closed end of the container to a level above the open end of the container, and being open at its junction with said closed end and it its junction with the cover, said blasting cap well having a closed end within the container, the other end of the blasting cap Well being open so that a blasting cap may be inserted in the canister, said cover closing the open end of the container and having an opening siugly receiving the Primacord well.

2. The canister of claim 1 in which the end of the Primacord well above the cover outwardly flared to lock the cover to the filled container body.

3. The canister of claim 2 in which the container body has an internal groove near its top and the cover an outwardly extending circular rib fitting said groove to aid in preventing removal of the cover when the end of the Primacord well has been swaged against the cover.

4. The canister of claim 3 in which the container body is cylindrical with a flat bottom and having its upper rim flared outwardly to a sharp edge beneath which is an annular groove and the cover has a reinforced rim fitting the flared rim of the container and has a downwardly extending circular flange with an annular rib extending outwardly to fit said annular groove in the cover positioned below the sharp edge.

5. The canister of claim 1 in which the wallof one of said wells has a plurality of longitudinal fins equispaced about its outer surface to insure that in forming such well of plastic, sufficient material will flow through the grooves in the die forming the fins to the closed end to provide a thickness of the well wall that will be thin enough to insurethat the primer material will be exploded but T be thick enough to insure against any holes in the wall which holes might permit primer material to enter the well as the primer material is being cast and thus interfere with entry of the blasting cap or the Primacord.

6. The canister of claim 5 in which the fins are integral splines extending continuously from the closed end of the container to a level adjacent the closed top of the blasting cap well, and the fins have a radial thickness of at least twice the thickness of the well wall between fins.

7. The canister of claim 6 in which the fins are four in number and are spaced apart.

References Cited by the Examiner UNITED STATES PATENTS BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL W. ENGLE, Examiner; 

1. A CANISTER FOR CAST PRIMERS SUITABLE FOR MASS PRODUCTION AND AUTOMATIC FILLING, COMPRISING A CONTAINER AND A COVER FOR THE CONTAINER; SAID CONTAINER BEING A ONE-PIECE BODY WITH AN OPEN END FOR RECEIVING THE PRIMER MATERIAL AND A CLOSED END, THERE BEING TWO WALLED WELLS IN THE CONTAINER, ONE TO RECEIVE A PRIMACORD PASSING LONGITUDINALLY THROUGH THE CANISTER AND THE OTHER A PARALLEL WELL TO HOUSE A BLASTING CAP, THE PRIMACORD WELL EXTENDING FROM THE CLOSED END OF THE CONTAINER TO A LEVEL ABOVE THE OPEN END OF THE CONTAINER, AND BEING OPEN AT ITS JUNCTION WITH SAID CLOSED END AND IT ITS JUNCTION WITH THE COVER, SAID BLASTING CAP WLL HAVING A CLOSED END WITHIN THE CONTAINER, THE OTHER END OF THE BLASTINGCAP WELL BEING OPEN SO THAT A BLASTING CAP MAY BE INSERTED IN THE CANISTER, SAID COVER CLOSING THE OPEN END OF THE CONTAINER AND HAVING AN OPENING SNUGLY RECEIVING THE PRIMACORD WELL. 